The present invention relates generally to a shell and tube heat exchanger for a multiple circuit refrigeration system.
Heat exchangers, such as condensers and evaporators, are utilized in refrigeration cycles to exchange heat between a heat transfer fluid (e.g. water, brine or air) and a refrigerant. A single refrigerant circuit can be utilized in the refrigerant cycle. However, if the compressor needs service and is shut down, the refrigerant circuit cannot operate. Therefore, it is beneficial for two or more refrigerant circuits to be utilized. One refrigerant circuit may be switched off, allowing the other(s) to operate at full capacity or if service is required.
In a prior shell and tube heat exchanger, heat transfer fluid passes through the heat exchanger in two passes. For example, in a two pass heat exchanger including two refrigerant circuits, the first portion of the first heat transfer fluid pass and the second portion of the second heat transfer fluid pass exchange heat with one refrigerant circuit, and the second portion of the first heat transfer fluid pass and the first portion of the second heat transfer fluid pass exchange heat with the second refrigerant circuit. A partition plate perpendicular to the axis of the shell separates the two refrigerant circuits.
There are several drawbacks to the prior art shell and tube heat exchangers for a multiple circuit refrigerant system. For one, when all of the refrigerant circuits are operating at a full load condition, the entropy generation (the destruction or availability of energy) is high due to a relatively larger temperature differential between the heat transfer fluid and the refrigerant. Secondly, the difference between the saturated discharge temperature and the saturated suction temperature (temperature lift) is also high. The temperature lift is representative of the compression ratio and hence the compression power requirement.
Hence, there is a need in the art for an improved shell and tube heat exchanger for a multiple circuit refrigeration system.
The present invention relates to a shell and tube heat exchanger for a multiple circuit refrigeration system.
A shell and tube heat exchanger of the present invention includes a plurality of tubes positioned within a shell. Heat transfer fluid flows through the tubes and exchanges heat with refrigerant flowing around the tubes within the shell. For example, in a two pass circuit design, heat transfer fluid enters through an inlet and exchanges heat in the first portion (first pass) of the first refrigerant circuit. The heat transfer fluid enters a heat transfer fluid box and then enters the second portion (second pass) of the first refrigerant circuit. In a three-pass design, heat transfer fluid leaving the second pass enters a third portion (third pass) of the first refrigerant circuit. The relative position of various passes may be one above the other, side by side, or any combination thereof.
Heat transfer fluid crosses over to the second refrigerant circuit through a center heat transfer fluid box. Heat transfer fluid then enters the first portion (first pass) of the second refrigerant circuit and continues to exchange heat. The heat transfer fluid again enters a heat transfer fluid box and then enters the second portion (second pass) of the second refrigerant circuit. Because each refrigerant circuit is separate, each side of the heat exchanger can have an unequal shell diameter and unequal tube counts to optimize capacity and the coefficient of performance
By employing a single heat transfer fluid circuit as described above, the average temperature difference between heat exchanging fluids can be reduced, reducing entropy generation and making the system more thermodynamically efficient. For the same amount of heat transfer area, the compressor power can be reduced significantly.
Accordingly, the present invention provides a shell and tube heat exchanger for a multiple circuit refrigeration system.
These and other features of the present invention will be best understood from the following specification and drawings.